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Photosynthesis Includes Two Main Processes As PSII and PSI

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Photosynthesis Includes Two Main Processes As PSII and PSI Photosynthesis includes two main processes as PSII and PSI. The process is underpinned by the light- driven water splitting reaction that occurs in PSII of plants, algae, and cyanobacteria. Solar energy is absorbed by chlorophyll and other pigments and is transferred efficiently to the PSII reaction center where charge separation takes place. This initial conversion of light energy into electrochemical potential occurs in the reaction center of PSII with a maximum thermodynamic efficiency of about 70%. In principle, it could drive the formation of hydrogen. Instead, the reducing equivalent is passed along an electron transport chain to PSI, where it is excited by the energy of a second ‘red’ photon absorbed by a chlorophyll molecule. In this way, sufficient energy is accumulated to drive the fixation of carbon dioxide, which not only requires the generation of the reduced ‘hydrogen carrier’, nicotinamide adenine dinucleotide phosphate (NADPH) but also the energy-rich molecule adenosine triphosphate (ATP) formed by the release of some energy during electron transfer from PSII to PSI (in the form of an electrochemical potential gradient of protons)[1]. In the Calvin cycle, carbon atoms from CO2 are fixed (incorporated into organic molecules) and used to build three-carbon sugars. This process is fueled by, and dependent on, ATP and NADPH from the light reactions. Unlike the light reactions, which take place in the thylakoid membrane, the reactions of the Calvin cycle take place in the stroma (the inner space of chloroplasts). This process is shown in Figure S 1 and Figure S 2. NADP+ CO2 Liquid water Excited Photosynthesis II Photosynthesis I NADPH+H+ Sunlight electrons Glucose Main product protons Calvine cycle Oxygen Waste(co- product) ATP synthase Biological process Photon Exergy ADP+Pi Chemical exergy Electrical exergy Gradient exergy Figure S 1. Qualitative Exergy-Flow Diagram of the plant. The Color Key describes the type of exergy flows between the different biological operations[2] Entropy 2021, 23, 3. https://dx.doi.org/10.3390/e23010003 www.mdpi.com/journal/entropy Entropy 2021, 23, 3. https://dx.doi.org/10.3390/e23010003 2 of 4 Figure S 2. Transfer of high energy electrons through photosystem II (PSII) and photosystem I (PSI)[3]. Two chemical reactions are described in this figure. All of the reactions are explained here. In the first step, water is split into protons, oxygen, and electrons. The electrons are excited to the high-level energy (P680*). NADPþ is reduced to NADPH. Intermediate carriers are various functional groups in the protein complexes of PSII and PSI. The first assumption of the model is based on Table S 1: Table S 1. The assumption for the average photon exergy Parameter Unit Value Avogadro’s number (NA) 6.023E+23 Planck’s Js 6.626E-34 constant (h) speed of ligh (c) m/s 300000000 λ_high(nm) nm 700 λ_low nm 400 T_earth(K) K 298.15 T_sun K 5762 B_photon_ave(kJ/mol photon) kJ/mol photon 212 Table S 2, Table S 3, Table S 4, and Table S 5 are the exergy analysis for photosynthesis and the Calvin cycle processes. Table S 2. Exergies and reduction potentials of PSII Redox standard Gibbs free standard change in Exergy Reactions potential energy change( electrical potential change (V) kJ/mol) (V) (J) 2→ +4 0.81 P680 1.1 -0.29 -671536 -819489 Entropy 2021, 23, 3. https://dx.doi.org/10.3390/e23010003 3 of 4 P680(required -0.8 1.9 4399716 4399716 exergy from sun) Pheo -0.6 -0.2 -463128 -463128 Qa 0 -0.6 -1389384 -1389384 Qb 0.1 -0.1 -231564 -231564 Cytb 0.19 -0.09 -208408 -208408 PC 0.37 -0.18 -416815 -416815 total differernce 0.37 -0.44 1018882 870928 Table S 3. Exergies and reduction potentials of PS Redox standard Gibbs free standard change in Exergy Reactions potential energy change electrical potential change (V) (kJ/mol) (V) (J) PC 0.37 P700 0.5 0.13 -301033 -301033 P700(required -1.3 -1.8 4168152 4168152 exergy from sun) A0 -1.3 -1.8 -694692 -694692 A1 -1 0.3 -486284 -486284 Fx -0.79 0.21 -138938 -138938 Fa -0.73 0.06 -324190 -324190 Fb -0.59 0.14 -92626 -92626 Fd -0.55 0.04 -46313 -46313 NADPH -0.53 0.02 -486284 -486284 total difference -0.32 0.21 1597792 1597792 total difference(NADPH -0.32 -1.13 2616173 2468720 -H2O) Table S 4. Exergy losses in the dark reactions Calvin Cycle reactions total exergy difference(δB(J)) 1: (5) + () → () +() 98582 2: + () +→2×() 322242 3 + 4: () + () + () → () + (3) 32746 + ( ) + 5: (3) → () 755 6: (3) +()→() 1974 7: () +→(6) + 57933 8: (6) + (3) → (4) +(5) 6035 9: (4) +()→() 2023 10: (7) + (3) → (7) + 62498 11: (7) + (3) → (5) +(5) 11187 12: (5) → (5) 1289 13: (5) → (5) 766 Entropy 2021, 23, 3. https://dx.doi.org/10.3390/e23010003 4 of 4 SUM 59803 conversion to glucose total exergy difference(δB(J)) ∗ 5 : (3) → () 189 ∗ 6 : () + (3) → () 987 ∗ 7 : () +→(6) + 28966 14: (6) → (6) 1298 15: (6) +→() + 31768 conversion to glucose SUM 63208 TOTAL SUM 661239 Table S 5. Overall chloroplast efficiency Inlet Outlet Loss Efficienc Overall PAR Reactions (kJ) (kJ) (kJ) y Loss(%) Loss(%) PAR Reflection 9977 9977 0 1 0 0 1322 1256 Non-PAR Reflection 661 0.05 61.33 6 4 Photosystem II 5319 4193 1126 0.788 5.5 14.45 absorption photosystem II ETC 5319 4074 1246 0.766 6.08 15.99 inlet photosystem I ETC 4209 2009 0.523 9.81 25.79 2200 ATP synthase 4901 2401 2500 0.49 12.2 32.09 Calvin cycle(Dark 1372 992 381 0.722 1.86 4.89 reaction) References [1] J. Barber, “Photosynthetic energy conversion: natural and artificial,” R. Soc. Chem. 2009, vol. 38, no. 1, pp. 185–196 |, 2009, doi: 10.1039/b802262n. [2] C. S. Silva, W. D. Seider, and N. Lior, “Exergy efficiency of plant photosynthesis,” Chem. Eng. Sci., vol. 130, pp. 151–171, 2015, doi: 10.1016/j.ces.2015.02.011. [3] M. M. C. David L. Nelson, Lehninger Principles of Biochemistry, Fourth Edi. W. H. Freeman, 2004. .
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